Hi all. I don't know how to describe my problem, but if you look at the surface of the sofa in the scene, there are few weird spots which left me clueless as to what it is and what cause it to happened.
I'm new to corona, and at the moment I'm pretty lazy to model my own scene just for that first test, so that's why I took the scene from the A4 Benchmark. I import the .obj file in max, and apply my own simple materials and lights setting to immitate the A4 Benchmark scene.
I attached together the material setting for the sofa. Render settings are left to default. Anyway, it was rendered at 4K for 7.5 hours with dual xeon, but single thread. Thank you.